Bug in lex?!?

[Esmond Pitt]

In article <14373 at hc.DSPO.GOV> siegel at hc.DSPO.GOV (josh Siegel) writes:
> (I have only tested this under SunOS 4.0 and BSD4.3)
>
> The following code makes lex produce C code with a syntax error in it:
> -----
> W	[ \t]+	
> %%
> ^{W}%	{ }
> %%

This also happens on a Pyramid under both att & bsd universes (i.e.
both lex's), probably because '%' is a special character to lex.
^{W}"%" also fails.

However the example works correctly & is in somewhat better (safer)
style if the definition of W is written as:

	W	([ \t]+)

Lex definitions should _always_ be parenthesised, for the same reason
that #defines which yield expressions should always parenthesise them:
to ensure that the apparent and real precedences are the same.

-- 
Esmond Pitt, Austec International Ltd
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